This project is an investigation of the significance and effects of interactions between epithelium and stroma during the transformation of epithelium from normal to neoplastic state. The systems currently being studied are: 1) Tumors of the submandibular salivary gland of mice, induced by polyoma virus; 2) Tumors of the forestomach and glandular stomach of mice, induced by a variety of chemical carcinogens. The general methods used involve neoplastic transformation of epithelium in the presence or absence of interaction with specific types of connective tissue (stroma). The results are evaluated on the basis of morphological and biological differences among the resulting neoplasms.